I. Field of the Invention
The present invention relates to wireless communication devices and systems, and more specifically, to a wireless device, such as a wireless telephone or modem, capable of communicating with both satellite and terrestrial communication systems.
II. Related Art
There are presently many different types of radiotelephone or wireless communication systems, including different terrestrial based wireless communication systems and different satellite based wireless communication systems. The different terrestrial based wireless systems can include Personal Communications Service (PCS) and cellular systems. Examples of known cellular systems include the cellular Analog Advanced Mobile Phone System (AMPS), and the following digital cellular systems: Code Division Multiple Access (CDMA) systems; Time Division Multiple Access (TDMA) systems; and newer hybrid digital communication systems using both TDMA and CDMA technologies. A CDMA cellular system is described in the Telecommunications Industry Association/Electronic Industries Association (TIA/EIA) Standard IS-95. Combined AMPS and CDMA systems are described in TIA/EIA Standard IS-98. Other communications systems are described in the IMT-2000/UM, or International Mobile Telecommunications System 2000/Universal Mobile Telecommunications System, standards covering what are referred to as wideband CDMA (WCDMA), cdma2000 (such as cdma2000 1xc3x97 or 3xc3x97 standards, for example) or TD-SCDMA.
An exemplary CDMA type satellite communication system comprises a constellation of 48 Low Earth Orbit (LEO) satellites and a plurality of ground stations (also referred to as terrestrial fixed stations or gateways). The gateways connect one or more known communication systems and networks to one or more satellite user terminals through the plurality of LEO satellites. Terrestrial based communication systems linked with the gateways can include, for example, telephony ground lines coupled with the Public Switched Telephone Network (PSTN), cellular and PCS systems, dedicated optical or microwave links, or the Internet. The satellite user terminals can be mobile, portable, or fixed terminals, as desired.
Typically, each satellite user terminal can receive and transmit to multiple satellites. This provides a desired level of satellite or spatial diversity. The satellite user terminals use such satellite diversity to improve satellite communication coverage by avoiding blockage of a line-of-site between the satellite user terminal and any given satellite. In some systems, the satellites serve only as frequency translators and repeaters. They may not contain or use specialized signal modulation or demodulation capabilities for changing the signal content, protocols, or structure. A signal transmitted from a user terminal to a satellite is referred to as a satellite uplink signal or frequency. A signal transmitted from the satellite to the user terminal is referred to as a satellite down link signal or frequency. From the perspective of the satellite being a bent-pipe or simple repeater, those signals traversing from the gateway to user terminals are referred to as forward link (communication) signals and those signals traversing from the user terminal to a gateway are referred to as reverse link signals (as viewed from the user terminal perspective).
The satellite converts the satellite uplink frequency (user terminal reverse link) into a gateway-satellite system forward link frequency, transmitted from the satellite to the gateway.
Also, the satellite converts the satellite down link frequency to a satellite system reverse link frequency, transmitted from the satellite to the user terminal (user terminal forward link). For example, if the user terminal down link frequency is 2500 Megahertz (MHz) and its uplink frequency is 1600 MHz, the satellite maps or translates signals at these frequencies to other desired link frequencies, such as 5100 MHz and 6900 MHz, respectively. Each satellite down link or forward link communication signal pattern has a series or set of xe2x80x9cbeamsxe2x80x9d (or sectors) illuminating a footprint on the surface of the Earth. A typical satellite might use sixteen such beams. Sometimes multiple beams at different frequencies are used to illuminate the same given area in a single xe2x80x9cbeamxe2x80x9d pattern, with each being referred to as a xe2x80x9csub-beam.xe2x80x9d
For CDMA communication systems using Pseudo-Noise (PN) or pseudo-random codes for modulation, each down link beam, and generally each satellite, uses a separate Pseudo-Noise (PN) code phase offset value for purposes of beam identification. Within each beam, orthogonal codes, such as Walsh codes, are used for beam or sub-beam channelization, creating a series of individual code channels for communicating with respect to each user terminal. In practice, the beams from one satellite form a footprint that can cover large geographical regions such as entire countries like the United Sates. The satellites receive the satellite uplink or reverse link communication signals from user terminals also using a series or set of beams (or sectors) in a pattern, typically sixteen. The forward and reverse link beam patterns need not be identical.
In an exemplary CDMA satellite wireless communication system, a common frequency, or set of frequencies defining the different beams, is used by each gateway transmitting to or through the satellites. Common radio frequencies allow simultaneous communication through multiple satellites to or from one gateway. Individual user terminals are separated by the use of lengthy or high chip-rate PN codes on the reverse communication signal link and orthogonal or Walsh Codes (and sub-beams) on the forward communication signal link. The high-rate PN codes and Walsh Codes are used to modulate signals transmitted from gateways and user terminal transceivers. Transmitting terminals (gateway and user terminal) may use different PN codes offset in time from one another (and/or Walsh codes), thereby producing transmitted signals that can be separately received at a receiving terminal.
Each of the gateways transmits a pilot signal having a common PN spreading code or code pair that is offset in code phase from the pilot signal of other gateways. Unique pairs of PN codes can be used to identify satellites within a particular orbital plane. Additionally, each gateway may have a unique identifying PN code and each down link beam (from a satellite to a user terminal) has a different PN code offset with respect to other down link beams for the satellite.
During system operation, a user terminal has a model of the satellite constellation and the user terminal is provided with a list of PN codes and PN code phase offsets for each satellite coming into or within view of the user terminal, or for gateways. Moreover, an outer PN code sequence, as described in U.S. patent application Ser. No. 09/169,358 entitled xe2x80x9cMulti-Layered PN Code Spreading In A Multi-User Communications Systemxe2x80x9d by Harms et al, and incorporated herein by reference, can be used to identify specific signal sources such as gateways or satellites.
This PN code can be used to derive a time and phase difference between satellites in view at any time, or having the same and/or different orbits. The user terminal is equipped with elements useful for acquiring and tracking beams from multiple satellites in multiple orbits simultaneously.
CDMA technology provides a mechanism for hand-off between satellite beams by changing PN codes used to demodulate or de-spread the received signals. Generally, this can be accomplished by using one or more codes in a set of codes, and changing the phase of the codes to match different code phase offsets used between different signal sources or beams. When more than one satellite is in view of a user terminal, the user terminal can communicate with the gateway through the more than one satellites. As a result, a call hand-off between satellites can be achieved at the gateway for the user terminal. This ability to communicate with multiple satellites gives the system satellite (also referred to as spatial) diversity. If trees, mountains or buildings block a satellite link to a user terminal, the user terminal can keep the communications link active by handing off to another satellite in view.
An exemplary satellite communication system is a global communication system with global roaming capability. Best communication results are achieved when there is a line-of-sight between a user terminal and a satellite. Preferably, the user terminal has an unobstructed view of a satellite. In cities and urban environments, such unobstructed views can be difficult to achieve. Moreover, a satellite terminal user may find it more convenient to use a radio telephone or wireless communication device, including wireless modems, inside a building.
Currently, a system user can achieve some level of mobile communication with global roaming capabilities for communication anywhere on the Earth using, in combination, an INMARSAT satellite terminal and a cellular phone. The INMARSAT satellite terminal is disadvantageously bulky and expensive, and fails to provide cellular interoperability. Therefore, the user is required to carry a second means of communication, that is, the cellular phone, which may not be operable in many areas.
Alternative systems are available to achieve global roaming using a satellite phone. However, such phones are expensive, relatively bulky, and require a large number of communication accessories.
Therefore, there is a need for a small, inexpensive mobile radiotelephone or wireless device that can operate with a satellite system and with terrestrial PCS systems and/or cellular systems, such as a CDMA cellular system, a TDMA cellular system, or an analog cellular system.
It is also desirable to minimize size, weight, and power requirements, and cost with respect to such a mobile wireless device or terminal.
The present invention provides a multiple band mobile radiotelephone (also referred to as a mobile radio and a Wireless Communication Device (WCD)) capable of communicating with both a satellite communication system and a terrestrial communication system. The satellite communication system can be a LEO satellite system. The terrestrial communication system can be a PCS/cellular system, including both analog and digitally based cellular systems. A cellular analog system can be AMPS. A digitally based cellular system can be a CDMA system. The WCD can concurrently receive signals from a terrestrial communication system and a satellite communication system. This is useful for receiving paging signals from the satellite communication system while communicating with the terrestrial communication system, and for satellite coverage monitoring.
The WCD includes a satellite communication transmit channel (also referred to as a satellite transmit channel) and a terrestrial communication transmit channel (also referred to as a terrestrial transmit channel). Each of these transmit channels includes an Intermediate Frequency (IF) section, a frequency up-converter or mixer, and a Radio Frequency (RF) section. The IF sections, the mixers, and the RF sections of these two transmit channels include common portions shared between the transmit channels.
The WCD includes a satellite communication receive channel (also referred to as a satellite receive channel) and a terrestrial communication receive channel (also referred to as a terrestrial receive channel). Each of these receive channels includes an RF section, a frequency down-converter or mixer, and an IF section. The RF sections, mixers, and IF sections of these two receive channels include common portions shared between the receive channels.
The WCD includes a first signal source to provide a first Local Oscillator (LO) reference signal to both the satellite and terrestrial communication transmit channels. In several embodiments, the first signal source also provides an LO reference signal to the satellite and terrestrial receive channels. A second signal source provides a second LO reference signal, independent of the first LO reference signal, to the satellite and terrestrial receive channels.
The above-mentioned common transmit channel portions and common receive channel portions, and independent local oscillators, permit the WCD to be advantageously constructed as a small, portable hand-held radiotelephone or wireless device. Therefore, the user of the WCD can conveniently carry a single, small device instead of, for example, two different devices: a terrestrial cellular and/or PCS phone, and a large expensive satellite phone for global phone coverage. This also applies to wireless devices that act as wireless modems or data transfer terminals, such as when used by portable computers.
As mentioned above, the present invention advantageously provides a small, inexpensive mobile transceiver that can operate with a satellite system and a terrestrial PCS/cellular system, such as a CDMA, TDMA or analog (for example, AMPS) cellular system.
The present invention has the advantage of minimizing cost, and minimizing size, weight, and power requirements, by sharing common signal paths and components in the mobile transceiver between different transmit channels and the different receive channels, as well as other advantages and characteristics.